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THE INFLUENCE OF BACKGROUND NOISE LEVEL AND SIGNAL DURATION ON THE JUDGED ANNOYANCE OF AIRCRAFT NOISE

A series of 72 flyover events were assessed by a jury of 35 observers, during 12 separate listening sessions conducted in a controlled test area designed to simulate typical indoor listening conditions. Each aircraft signal was superimposed on a controlled random traffic background signal having a duration exceeding that of the aircraft event. The presence of a steady mean traffic background noise can reduce the perceived noisiness of aircraft flyover events, provided that the judgment time available is sufficiently greater than the event time (time in excess of background). For a given peak event level, a reduction in associated background noise of 21 dBA is shown to be equivalent subjectively to an increase of 5.5 dBA in peak event level, with fixed background conditions. Although regressions obtained with the noise pollution index, L sub NP, for single event judgments generally showed a lower correlation than the L sub o and L sub p - L sub o regression variables, the score data did show a number of significant trends which are also associated with the LNP index variations computed for single noise events.